[iOS] Remove first responder experiment

Experiment caused problems on iOS 12 and 14. On iOS 12 input accessory
views had a bug where they were not being added most of the time. On
iOS14 a divergence on some usage was observed in UMA, but there is no
clear explanation for this.

Bug: 816427
Change-Id: I98441836d208a30e5ea270c84e23f50b320eba52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2565696Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Javier Flores <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832360}

ios/chrome/browser/ui/ui_feature_flags.cc

@@ -31,9 +31,6 @@ const base::Feature kForceUnstackedTabstrip{"ForceUnstackedTabstrip",
 const base::Feature kTestFeature{"TestFeature",
                                  base::FEATURE_DISABLED_BY_DEFAULT};
 
-const base::Feature kFirstResponderSendAction{
-    "FirstResponderSendAction", base::FEATURE_DISABLED_BY_DEFAULT};
-
 const base::Feature kEnableNativeContextMenus{
     "EnableNativeContextMenus", base::FEATURE_DISABLED_BY_DEFAULT};
 

ios/chrome/browser/ui/ui_feature_flags.h

@@ -34,9 +34,6 @@ extern const base::Feature kForceUnstackedTabstrip;
 // features in tests works.
 extern const base::Feature kTestFeature;
 
-// Verify if the crash in https://crbug.com/816427 is fixed on iOS 12.
-extern const base::Feature kFirstResponderSendAction;
-
 // Feature flag that enables the native UI Context Menus (not for Web content).
 extern const base::Feature kEnableNativeContextMenus;
 

ios/chrome/browser/ui/util/uikit_ui_util.mm

@@ -33,22 +33,6 @@
 #error "This file requires ARC support."
 #endif
 
-namespace {
-
-// Store a reference to the current first responder.
-UIResponder* g_first_responder = nil;
-
-}  // namespace
-
-// Category used to get the first responder.
-@implementation UIResponder (FirstResponder)
-
-- (void)cr_markSelfCurrentFirstResponder {
-  g_first_responder = self;
-}
-
-@end
-
 void SetA11yLabelAndUiAutomationName(
     NSObject<UIAccessibilityIdentification>* element,
     int idsAccessibilityLabel,
@@ -315,18 +299,6 @@ UIView* GetFirstResponderSubview(UIView* view) {
 
 UIResponder* GetFirstResponder() {
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
-  if (base::FeatureList::IsEnabled(kFirstResponderSendAction)) {
-    DCHECK_CURRENTLY_ON(web::WebThread::UI);
-    DCHECK(!g_first_responder);
-    [[UIApplication sharedApplication]
-        sendAction:@selector(cr_markSelfCurrentFirstResponder)
-                to:nil
-              from:nil
-          forEvent:nil];
-    UIResponder* firstResponder = g_first_responder;
-    g_first_responder = nil;
-    return firstResponder;
-  }
   return GetFirstResponderSubview([UIApplication sharedApplication].keyWindow);
 }